A propeller pump or an axial flow pump comprises an axial inlet and an axial outlet surrounding the housing of a drive unit of the pump. In addition, the pump comprises a hydraulic unit comprising a propeller rotationally supported at an intermediate position, close to said inlet. Propeller pumps are in general vertically arranged in and located at the lower end of a discharge pipe of a pump station. Said lower end of the discharge pipe is arranged close to the bottom level of a liquid holding tank of the pump station. It is important that the flow of liquid entering the propeller pump is uniform, i.e. that the speed of the flow of liquid is uniform, or only has a small relative deviation, across the entire cross section area of the propeller pump at the level of said propeller. If the flow of liquid is not uniform, great mechanical stress will act upon the propeller and the propeller vanes.
Reference is now made to FIG. 6, which discloses an embodiment of a prior art pump station. In the shown embodiment, a pump station, generally designated 100, comprises a liquid holding tank 101, an inlet pipe 102 and three axial flow pumps 103. Seen from above the pump station 100 has an elongated rectangular shape, the three pumps 103 being located along one of the short sides of the liquid holding tank 101 and the inlet pipe 102 being located in a long side of the liquid holding tank 101 at the other end of the pump station 100. The liquid holding tank 101 may be separated in a first section known as fore bay 104 and in a second section known as pump bay 105, the latter comprising said pumps 103. When liquid enters the pump station 100, through the inlet pipe 102, the liquid is turbulent and a rotating flow of liquid 106 arises in the fore bay 104. It would be very harmful for the pumps 103 if such a rotating and turbulent flow would be present adjacent the inlet of said pumps 103, due to pressure differences. Thus, it is important that the flow of liquid entering the pump 103 is steady and uniform. One known way of creating a steady and uniform flow of liquid is to build a large fore bay 104 and a separate cell 107 for each pump 103, such that the rotating flow of liquid 106 is broken and a straight and uniform flow of liquid enters each pump 103. The cells 107 are delimited by dividing walls 108. One drawback of pump stations arranged in the described way is that they are space requiring, i.e. that the length of the pump bay 105 is three times longer than the required length of the pump bay associated with the inventive intake device. The size of the fore bay 104 may also be decreased when using the inventive intake device.
A known way of setting up a more compact pump station, regarding the required area/volume, is to use an intake device according to the preamble of claim 1. Such an intake device is arranged to be used instead of or as a complement to the abovementioned cells 107. Hereinafter, a prior art intake device is located in an opening at the bottom of a wall of the liquid holding tank. Known intake devices have good function when used in pump stations, in which the liquid is steady and the flow of liquid towards the propeller pump is directed straight into said intake device. However, in pump stations or applications in which the flow of liquid is rotating, for example, i.e. that the main flow in the liquid holding tank is directed across the wall, in which the intake device is arranged, the flow of liquid will swirl into the intake device and will not be uniform when reaching the propeller due to turbulence in the intake device. In order to solve the latter problem the intake device may be made longer, i.e. such that the flow of liquid has a longer way and time to get uniform. However, this solution entails larger costs as well as a larger pump station.